1. Field of the Invention
The present invention relates to a photomask used for photolithography which is performed in manufacturing a semiconductor device, a liquid crystal display device, and the like, a method for detecting a pattern defect of the photomask, and a method for making patterns using the photomask.
2. Description of the Related Art
In manufacturing a semiconductor device, a liquid crystal display device, and the like, various kinds of patterns formed on a photomask are transferred by photolithography to a photosensitive resist formed on a substrate. After this transfer, the photosensitive resist is developed to process a wiring layer and the like with the patterns on the photosensitive resist as a mask.
Therefore, extremely high accuracy is required for the photomask. Thus, inspection of the photomask itself using a defect inspecting apparatus for the photomask, inspection of the patterns formed on the photosensitive resist by the transfer using a defect inspecting apparatus for a wafer, and the like are performed. The latter inspection is performed mainly for a photomask such as a Levenson phase shift mask whose defect cannot be guaranteed to be detected when only the pattern defect inspecting apparatus for the photomask itself is used. The defect of the photomask is detected from a defect in the patterns formed on the photosensitive resist by the transfer.
However, on the photomask used in manufacturing the semiconductor device, the liquid crystal display device, and the like, patterns such as a memory cell array, a logic circuit, and a latch circuit are formed with slight gaps therebetween. Accordingly, even in a region inside a scribe line, a region where the patterns are dense and a region where the patterns are interspersed exist irregularly. If defect inspection for inspecting whether or not the mask patterns include the defect is performed for such a photomask using an existing pattern inspecting apparatus, the existence of the defect is recognized even in a location where the defect does not exist, in some cases. This defect is sometimes called a dummy defect.
The occurrence of the dummy defect is caused by an inspection algorithm of the pattern defect inspecting apparatus. The pattern defect inspecting apparatus performs alignment of the patterns while inspecting the patterns. The alignment is indispensable processing because an extremely minute deviation exists compared with design data in the patterns formed on the photomask and the deviation is inevitable. However, if a region where the patterns do not exist at all is scanned, the alignment is not executed normally because of the aforesaid inspection algorithm, which leads to mix-up. As a result, when a scan target is shifted from such a region to a region where the patterns exist, normal patterns are recognized as the defect.
FIGS. 12A, 12B, and 13 are schematic diagrams showing a location where the dummy defect occurs. FIG. 12B substantially corresponds to a region surrounded by a circle in FIG. 12A, and FIG. 13 substantially corresponds to a region surrounded by a circle in FIG. 12B.
As shown in FIG. 12A, it is supposed that there is a photomask in which, for example, five rectangular pattern-dense regions 102a to 102e exist in a region surrounded by a scribe line 101 and no pattern exists at all between them. More specifically, as shown in FIGS. 12A and 12B, pattern-dense regions 102b and 102c are arranged side by side along a longitudinal direction of the pattern-dense region 102a and gaps having a T-letter shape exist between these three pattern-dense regions. Further, as shown in FIG. 13, patterns having an F-letter shape densely exist near a corner of the pattern-dense region 102b which is the closest to the pattern-dense regions 102a and 102c. 
As shown in FIG. 12B and FIG. 13, if such a photomask is scanned for inspection in a direction from the right to the left in the drawings, mix-up of alignment does not occur and normal pattern inspection is performed during when the pattern-dense region 102c is scanned and thereafter a region between the pattern-dense regions 102c and 102b is scanned. However, when a scan region is shifted from the region between the pattern-dense regions 102c and 102b to the pattern-dense region 102b, the dummy defect occurs at a side A where the pattern initially appears as shown in FIG. 13.
The problem of the dummy defect as described above occurs not only in inspecting the patterns on the photomask itself but also in inspecting the patterns formed on the photosensitive resist by the transfer. In other words, also in a case of inspecting the defect in the patterns formed on the photosensitive resist, alignment is not normally performed when the region where no patterns exist at all is scanned, and the normal patterns are recognized as the defect when the scan target is shifted from such a region to the region where the patterns exist.